Today, many forms of information are converted from a digital form to an analog form, such as video information displayed on people's televisions. Thus, an example of such information is digital television (DTV) information. Converting digital information to analog information typically involves the use of a digital-to-analog converter (DAC) contained within a video digital signal processing chip. The input of the DAC is typically coupled to a digital information source, such a digital television feed provided by a cable service provider. The output of the DAC is typically coupled to a display such as a television or a computer monitor. DACs are typically implemented using, among other things, transistors contained within an integrated circuit chip. As the DAC ages, however, performance of the DAC can decrease due to, for example, degradation of n-p junctions contained within the transistors.
DAC operation can also be affected by defects caused during the manufacturing process of the DAC. For example, copper precipitates and pitting are common manufacturing defects. During the manufacturing process of DACs, integrated circuit chips containing a DAC are subjected to a series of diagnostic tests designed to determine if operation of the DAC is within acceptable tolerances. If the operation of the DAC is not within acceptable tolerances, typically the entire chip is discarded. If the DAC is part of a larger digital signal processing (DSP) chip, the costs associated with discarding an entire chip can be substantial.
DACs typically convert an incoming digital signal to an analog signal using multiplication. DACs typically multiply each incoming digital word of a digital signal by a reference voltage and a gain factor. For example, the operation of a DAC can be simplified and represented as:{DAC output}=(G×D×Vref)/2n,  (1)
where G is a gain factor, D is a digital input word, Vref is a reference voltage, and n is the resolution of the DAC. Alternatively, a reference current can be substituted for the reference voltage.